Add config option to hide header tabs on certain pages

[nateKlaux]

Feature Description

In the metadata of an article / mdx file, add an option to hide the header tabs of a navigation bar.

Use Case

Use this option this to create more customizable landing pages.

Proposed Experience (Optional)

In an article's metadata:

---
title: Article title
hide-header-tabs: true
---

And it'd render:

Alternatives Considered (Optional)

Currently, I have client side Javascript that sets the display of nav.fern-header-tabs to none and the height of .fern-theme-default.fern-container .fern-header-container to auto, but the nav bar still flashes momentarily.

This is unideal though and occasionally the nav bar hides too slowly and users notice it disappear.